Self-synchronous positional control system



J 29, 7- k E. J. ISBI STER ET AL- ,56

SBLF-SYROHROIDUS POSITION CONTROL SYSTBI Filed 4 i'v', 1939 3 She'ota -Sheot 1 y 1947- E. J. ISB ISTER ET AL SBLF-SYNCHRONOUS POSITIQNAL CONTROL SYSTBX Filed Nov. 1'7, 1939 3 Sheets-Sheet 2 murms Ema J Asap-YER an gums L. Nose-LE) WM uly 29, 9 E. J. lss ls'rsk El AL 2 SELF-SYNCHRONOUS POSITIQRAL CONTROL- SY STBI mm Nov. 17, 1939 '3 sham-sheet s INVENTGB 4 1 Mm fibula);

[gm .1 lie/ans an? Patented July 29, 1947 SELF-SYNOHBONOUS POSITION CONTROL SYSTEM ErioJ.Isblstor,Brooklyn.N.!.,andFranoisL.'

Moseley. Chevy Chase, Md

Gyroscope BEISSUED not 31 esoassignorstosparry Application November 17, im, Serial No. 304,095

1: Claims. 1

This invention relates generally to electrical control systems and the invention has reference. more particularly, to a novel electrical positional control system wherein a turnable controlling object is arranged to operate through suitable electrically operable means to cause a controlled object to turn in substantial synchronism with the controlling object, said electrically operable means employing a pair of signal voltage transmitters or synchronous generators operating in diilerent speedratios, l. e., a fine or high speed transmitter and a, coarse or low speed transmitter. corresponding receivers being employed adjacent the controlled object and operating through a novel servo system for determining the motion of the controlled object.

To obtain great accuracy oi reproduction by the controlled object or motion of the controlling object, 1. e., substantial synchronism oi the ob- Jects, it is necessary to employ a fineor high speed signal voltage transmitter and connected receiver arrangement. This high speed arrangement may operate in a ratio, for example, of 36: 1 providing one channel of the synchro transmission system. The other channel 01' the transmission system is connected in a 1:1 ratio inasmuch as the objects may get out of step any amount from zero to 180 in either direction due, for example, to the turning oi the controlling object such as a handwheel. when the system is not in operation.

The principal object of the present invention is to provide a novel position control system employing high and low speed transmitter-receiver arrangements and a remote servo system controlled therefrom for operating a controlled ob- ,ieot in synchronism with the low speed transmitter, and wherein the power supply to the transmitter and receiver arrangements is independent 01' that provided for the remote servo system, whereby the servo system may be operated from a local source or A. 0. supply.

Another object 01' the present invention is to provide a novel type oi position control system wherein means is provided for eliminating 180' ambiguity oi'the controlled object with respect to the operation of the transmitter arrangement. 1. e., means is provided for preventing the controlled object from coming to rest 180 out of Phase with the controlling object.

A further object oi the present invention is to provide a position control system employing modulator means for converting a reversible A. 0. signal into a reversible D. 0. signal, and for thereafter reconverting mid reversible D. C. signal into m an Brooklyn. N. in, a I

a reversible A. 0. signal ior use in controlling the servo system.

A further object of the present invention is to provide a novel positional control system wherein not only the displacement signal is used in controlling the controlled obiect, but also rate signals adapted to include velocity and acceleration are employed in conjunction with the displacement signal, thereby obtaining a highly refined system of control. 1

Other objects and advantages will become apparent from the specification, taken in connection with the accompanying drawings wherein the invention is embodied in concrete form.

In the drawings.

Fig. 1 is a wiring diagram illustrating a preierred form of the novel position control system of this invention.

Fig. 1A illustrates a portion of the circuit 01' Fig. 1 somewhat modified.

Fig. 2 is a diagram illustrating the potentials involved in the output of the transmitters of Fig. 1.

Fig. 8 is a detail view for use in explaining Fig. 2.

Fig. 4 is a view'simllar to Fig. 1 but of a somewhat modified form of the invention.

Referring now to Figs. 1 to 3 of the drawings. the controlling object I is illustrated as a handwheel. although the some might be any small power turned object, such as a telescope, the angular position of which is to be accurately and immediately repeated by the controlled object 2 which may be a ponderable turnable object.

The high and, low speed transmitting devices 8 and 4, respectively, and their remote connected receiving devices I and l, respectively, may be of any suitable type. Preferably, these devices are oi. .the A. C. type in which the transmitting and receiving devices are similar in construction and are each provided with a poly-circuit armature winding and a single circuit field winding. In the drawings. these devices are each provided with a three-circuit armature winding I physically similar to a three-phase star connected armature winding. This armature winding may be mounted on the stator while the field winding I is on the rotor. In connecting each receiving device to its respective transmitting device, three conductors are used by means oi which like points of the two armature windings I of the devices are interconnected.

The field windings 0 oi the transmitter are connected to a suitable source of A. C. supply led through the single phase leads 9, which supply amass 3 may be from a local source, if desired. l 'ield winding l of the high speed transmitter I is connected to handwheel I through reduction gearing III, whereas field winding I of the low speed transmitter 4 is connected to turn at the same rate as the handwheel I.

Transmitter field windings I produce in their respective armature windings I alternating magnetic fields having positions in space determined by the relative positions of windings I with respect to windings 8. Any rotation of the transmitter field windings or rotors I caused by angular movement of handwheel I produces a corresponding angular shifting of the axes of the magnetic fields of their respective armature windings resulting in a corresponding shifting of the fields of the armature windings I of the receivers l and 8, thereby tending to cause field windings I of the receivers to follow up such shift, but since these field windings are mechanically connected by the mechanical follow-up transmission I! to the controlled object 2, alternating E. M. E's are induced in the field windings 8 of receivers I and 6, the values of which E. M. F.s are substantially proportional to the angular displacement between the handwheel I and object I, i. e., for small angular displacements.

The A. C. signal voltage induced in field winding 8 of the high speed of fine receiver 5 is limited by a voltage limiter II which is a non-linear resistor made up, for example, of selenium or copper oxide discs connected back to back so as to pass A. C. The use of this voltage limiter is disclosed in copending application, Ser. No. 41,851, wherein Francis L. Moseley, one of the present applicants, is the inventor. The limited voltage of the fine receiver 5 is added in the series with the signal voltage output of the low speed or coarse receiver t and with a fixed signal voltage supplied through the secondary winding ii of a transformer If that is energized through leads a from supply 9. This summation voltage issupplied to the primary of'a transformer it having a center-tapped secondary connected to. supply the summation or combined signal and fixed voltages to the grids of a double triode amplifier ll connected in push-pull. The output of the amplifier I5 is fed through its plate transformer II to a modulator II shown as of the ring type employing dry disk rectifiers which may be of the selemmn oxide type. This modulator is also supplied with A. C. carrier voltage from transformer II which voltage, of course, passes through resistor I8 and II and through the divided sec- .ondary windings of the transformer I.

As hereinafter more fully pointed out, the modulator II functions as a full wave rectifier. Assuming that the input signal, that is, the voltlse supplied to the rectifier from the secondary of transformer II has a 60 cycle frequency and also that the carrier or reference voltage supplied to the modulator from secondary ll of transformer is of the same frequency, the output of modulator II will comprise components having frequencies corresponding to the sum and difference of the signal input and reference or carrier frequencies. Hence, the output componentsinthemodulatorwillbe of 120 cycles and zero cycles, the latter, of course. being the D. C. component. The 120-cycle component is readily suppressed or eliminated by the filter network with which the output of the modulator is connected, as described below.

The modulating carrier signal supplied from transformer It combines with the signal voltage suppliedfromtubellinthemodulatorllto' produce a pulsating D. C. signal, the magnitude of which is proportional to the magnitude of the alternating current signal fed from tube II and the polarity of which reverses with reversals of phase of the A. C. signal. The 120 cycle pulsating component in the output of the modulator II and existing across the outer ends of resistors II and II is filtered out by the filter network consisting of inductances II and II and condenser The ring type modulator i1 provides, of course, for full wave rectification of the amplified A. C. signal voltage output of tube II, thereby providing a 120 cycle modulated voltage instead of cycles. This is desirable because in a high performance control circuit such as this, only a little filtering can be tolerated as any appreciabl time delay introduced by a filter would make the controlled object rough and unstable in operation. It is understood. however, that other types of modulators could be used such as push-pull triode vacuum tube modulators especially in slower acting controls.

The D. C. output applied across the terminals of condenser 21 is supplied to a second modulator 28 also shown as of the dry disc rectifier ring type modulator. The carrier A. C. for this rectifier II is supplied from the servo motor power circuit source; this being, for example, a local three-phase source having the three-phase leads 24, 2|. and 28, leads 2 and It supplying a transformer II, the secondary winding 2. of which supplies the modulator 23. The reversible D. C. signal input to modulator 23 combines with the carrier signal from winding 21 in the modulator 23 to produce an A. C. output across the primary of transformer II, that is Pr p rtional to the magnitude of the controlling A. C. signal. The phase of this A. C. output applied to transformer II reverses when the phase of the controlling signal reverses, although these two signals may be of different frequencies. As the carrier of the second moduhtor, i. e., modulator I8, is related definitely to the servo circuit power source, the phase of the modulator output signal has the necessaryand correctphaserelationtotheA.C. plate voltage of the double triode tube II.

Tubellservesasanamplifierandalsoasa rectifier in that it draws current from secondary 82 through the impedance consisting of the choke coil 33 and resistors 34 and ll. the current from the secondary I2 dividing at the mid-tap of choke coilflsothatpartofthiscurrentfiowsthrough one-half of coil 33 and through resistor 34, whereas the remainder fiows through the other half of coil 88 and resistor 8|.

when the displacement sltnal is being amplified by tube II, the currents fiowing in the two halves of the choke coil as will be unequal because of the phase relations between the A. C. plate supply to tube II and the A. C. sisnal potential supplied to the grids thereof. i. e., when thesignaipotentialisofonephasaonebfthe plate circuits of tube ll draws a large current,

78 tive displacement. The presence of this D. C.

component in choke coil it, due to the resistance or its windings,'causes a voltage drop across the choke coil and the same is true to a much larger extent of the resistors 84 and 8', the said total voltage drop being in phase with the displacement and proportional if this D. C. component varies, a voltage is induccd across the choke coil II, which induced voltage is in phase with the time rate of change of displacement, i. e..v velocity, the first derivative of displacement with respect to time.

In this way, if the relative displacement of the objects. I and 2, is changing, two D. C. voltages appear across the outer ends of resistors 04 and 85, one proportional to and in phase with the relative displacement of the objects and the other proportional to and in phase with the relative velocity. In addition there exists an A. C. component across these resistors proportional to the displacement voltage.

The networks comprising condensers It and 81 and resistors and 39 to which these voltages are applied take the derivative thereof provided these voltages are changing. Thus, if the relative displacement of the objects is not changing, neither of these voltages will be present and if the relative displacement is changing uniformly only one, the first derivative of displacement with respect to time, will appear but if the relative displacement of the objects is changing with acceleration or deceleration, both voltages will appear. This rate circuit is disclosed in the copending application of Francis L. Moseley et al., Ser. No. 11,424, filed March 16, 1935.

Condensers 38 and 31 cooperate with resistors 38 and 39 in applying displacement and rate voltages to the grids of grid control rectifier tubes 40 and I, the output of which tubes pass through windings of the transformers l2 and 43 having their other winding connected in circuit with the windings it and 45 of the reversible capacity type induction servomotor 46.

In operation, as the handwheel i is turned, the

outputs of the high speed or fine transmitterreceiver is combined with that of the low speed transmitter-receiver and with the fixed voltage from the transformer secondary winding i I in the manner illustrated in Figs. 2 and 3. The voltages shown in Fig. 2 are the R. M. 8. (meter) values of the various voltages and are applied against the angular position of the controlled object with respect to the controlling object. Voltages applied below the horizontal or X-axis are to be understood to be 180 out of time phase with those a plied above this axis. If the summation voltage reverses its time phase, the controlled object reverses its direction of rotation.

Curve Vi shows the open circuit voltage across the receiver rotor l of the 36:1 transmitter-receiver device. It will be seen that this voltage has a zero every 5. The phase relations are such, however, that so far as this voltage alone is concerned, the controlled object will synchronize only at the even zero points, i. e., 0, 10, 20, etc., degrees.

Curve Va shows the open circuit voltage of the 36:1 receiver rotor 8 as limited by the voltage limiter 3|. It will be noted that the peaks of the voltage curve V1 are removed giving the flattopped wave form shown as Va. The voltage limiter Si is so adjusted that the peak value of the limited signal is always less than the value of the 1:1 signal at :5 from zero.

Curve V: shows the open circuit voltage or the 1:1 transmitter-receiver device. This curve has only two zero points per revolution of the conto the magnitude thereof.

object i always driven to the zero degree point. o

If the limited 36:1 and the 1:1 signals were :ogrbined and applied to the control of the obiect en namely, zero and 180". It will be seen from the phase relations of the 86:1 signal that it tends to hold' the controlled object on the 180' point as well as the zero degree point, and if the controlled object is within a few degreesof 180. it would overpower the 1:1 signal and keep the object at the 180" point of synchronization. This 180 ambiguity is eliminated, however, in the present case by adding the fixed A. through transformer winding ii in series with the 1:1 signal. This fixed additional voltage is designated Vt in Figs. 2 and 3, and gives the 1:1 signal voltage a zero at zero degrees and at 176, as shown in Fig. 2. and adds in the proper phase relation with the limited 38:1 signal to give only one point of synchronization for the controlled object, namely, the zero degree point. Th sero signal point at 175 shown in Fig. 2. is an unstable zero, and our endeavor to hold the controlled object at this point is like trying to balance a needle on its point which is practically impossible since the controlled object tends to move from this point in a direction depending upon the resultant voltage.

The combined signal from the synchronizing circuit is amplified by the vacuum tube II and fed through its plate transformer it to the phase modulator i! which converts this A. C. reversible amplified signal voltage to a reversible D. C. voltage. The carrier voltage supplied by transformer secondary winding 84 must be equal to or greater than one half the maximum value of the signal voltage output of transformer is in use. Assuming that the left-hand end of the secondary 84 of transformer i2, supplying the carrier signal to modulator I1, i positive for the moment, then current from thi secondary fiows through the upper half of the secondary of transformer it, through rectifier 80 and resistor it, back to winding 64. At the same time, current from winding 64 fiows downwardly through the lower half of the secondary of transformer it, through rectifier 81 and resistor i8, back to winding .4.-

At this time, no current flows through rectifiers 6i and 83.

As the carrier currents in the two resistors is an is are equal and flow in opposite directions, there i no net voltage across the outer ends of these resistors due to the carrier current. As-

suming also that at the moment the left-hand end of transformer winding 84 is positive the handl i is being turned in such direction that the signal voltage from tube ll makes the upper end of the secondary of transformer l8 positive, in that case the signal and carrier currents are additive in rectifier so and resistor is. This signal current flows from resistor is through winding 64, back to the upper half of the secondary of transformer it. Also, signal current from the lower half of the secondary winding i8 is subtractive from the carrier current in rectiher 82 and in resistor it. Since the carrier current is larger than the signal current, the signal current from the lower half of the secondary of transformer is may be considered as fiowing through winding 84, upwardly through resistor i8 and reversely through rectifier I! back to the lower hall of the secondary of transformer it. In other words, this signal current is subtractive 8 t tailed oblcct and phase relations are stich'that we would have only two synchronous points,

C. voltage supplied ingfltotake -from the carrier current fiowing upwardly through rectifier 62. S nce the carrier and signal currents are additive in It and subtractive in II, there is a net D. C. voltage across the outer ends of resistors II and it, which voltage is war. tional in magnitude to the signal voltage appearing across the secondary of transformer II, the current fiow through these resistors being such that the outer or lower end of resistor ll is positive with respect to the outer or upper end of resistor ll.

During the next half cycle of the applied voltages when the left-hand end of winding 84- andthe upper end of the secondary of transformer ll become negative, the operation is similar, except that rectifiers II and I2 conduct current instead of rectifiers Ill and 02. Although the direction of the carrier current flow is reversed in the resistors II and II, the direction of fiow of the current due to the signal voltage is the same as in the previous half cycle, the lower end of resistor ll remaining positive with respect to the upper end of resistor II. Thi will be apparent when it is noted that the signal current from the upper half of the secondary of transformer ilfiows through winding '4, up through resistance l8, and through rectifier 22, back to the upper end of the secondary of transformer It. Also, at this time current from the lower half of the secondary of winding ll fiows reversely through rectifier 6i, i. e., is subtractive from the larger carrier current flow therethrcugh, fiows up through resistor II, and through winding N, back to the secondary of transformer ll. Thus, it will be seen that the signal current fiows upwardly in both resistors II and II, showing that the lower end of resistor it has the higher potential just as in the previous half cycle. In other words, the carrier current merely operates as a switching means for causing the rectifiers to operate alternately in pairs to pass current as desired.

If the direction of the handwheel l is reversed,

then in that case the output of the secondary of transformer-l8 is reversed. Thus going back to the first example, when the left-hand end of winding 64 is positive, the upper end of the secondary transformer It will be negative and if the circuits are traced through, it can be shown that the resultant D. 0. signal current fiows downwardly through resistors I! and It, thereby making the upper outer end of resistor ll positive with respect to the lower outer end of resistor i2, hence reversing the directlonof oper: ation of the motor 48.

The reversible D. C. voltage across resistors It and i9 is applied to the second modulator 22 which reconverts the reversible D. C. signal to a reversible phase A. C. signal for application to the grids of the rate amplifier tube It, the output of which in combination with the rate circuit disclosed, controls the grid controlled rectifier tubes 40 and ii to determine the operation of the capacity type or two phase induction motor 4 driving the controlled object 2. when tube II is passing current, transformer 42 is shorted, in effect, and winding 44 takes a current in phase with that of the supply 2l2l, whereas winding 45, the current of which passes through condenser 51, takes a current substantially 90 leading that of leads 24-25, so that motor It operating as a two phase motor turns in one direction. On the other hand, when'tube Ii is passing current, transformer 48 is shorted, in effect, causing winda leading current while winding takesacurrentinphasewlththatofleads 2land2lcausingmotorlltoturnintherererle direction. The follow-back connection ll serves to re-position the windings I to the null positionwhentheobiects are in synchronism.

If desired. condenser ll can be replaced by a smaller condenser ll shown in l'lg. 1A. connectingtheplatescftubesllandllinwhich case the transient eliminating resistance I may beleftoutsincethecondenserl'l'alsose'rvesthe function ofthis resistance. The operation is substantially the'salne. i. e., when tube ll is passing current the econdary of transformer 42 is shorted in effect, and condenser II is connected across the secondary of transformer 48 aothatthistransformertakes aleadingcurrent causinginotorwindinglltoalsotakealeading current.

Inasmuchasthecondensermotorllinopcrating causes the plate voltage on the non-operatingtube ilorlLasthecasemaybatoshift phase merely 90 as the motor operates in one direction or the other, it is desirable to employ acondenserllasshowninl'lg. lAconnected across the grids of tubes I, ll. In this case. the resistances l and I should be inserted between the grids of these tubes and condensers I! and 21. This has the effect of placing condenser II and one of the resistances I or II, as thecasemaybeinserieewiththegridofthe non-operating tube thereby shifting this grid voltage to-correspond with the shift in its plate voltage.

In the form oi invention shown in Hg. 4, parts similar to those in Fig. l, are similarly numbered. In this form of the invention, the apparatus is thesame'asthat showninl'ig. Luptothesecond modulator, but in the present figure instead of using the dry disc rectifier ring type modulator for converting the reversible direct current signal to a reversible phase A. C. signal, a pushpull thermionic modulator is employed. This modulator consists of tubes 48 and 40 having their grid filament circuits supplied with A. C. from transformer I energized by leads II and '2 of the three-phase supply ll, 52, and II. which supply may be a local supply, obtainable at the controlled obiect. The output of the phase modulator I1 is applied through the filter 20, 2| and 22 to the grids of modulator tubes 4|, II, the output of thesev tubes being supplied as in the case of modulator 22 of Fig. l to the rate taking tubes 3| and II. A reversible repulsion motor 48' is used in Fig. 4 in lieu of the split phase motor I of Fig. 1. The field winding I of this motor is connected to supply leads ll, ll, whereas the pairsoi'brushesofthismotorareconnected across windings of transformers l2 and ll. Field winding '4 induces A C. potential in the rotor of motor ll so that potentials appear across the brushes of this rotor which are applied to transformers l2 and 2. Thus, whenthe tube ll is rendered conducting, the corresponding winding of transformer 42 is shorted, in effect, and motor 48 operates in one direction, whereas when the tube is rendered conducting the corresponding winding of transformer 42 is shorted, in efiect, and motor 48 operates in the opposite direction. the speed of operation of the motor depending upon the magnitude or the current fiowing in the tube outp t circuit.

Asmanychangescouldbemadeinthe above construction and many apparently widely different embodiments of this invention could be made withoutdopartingfromthescopethereof,itis

asses intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted a illustrative and not inalimiting sense.

Having described our invention, what we claim and desire to secure by Letters Patent is:

l. A position control system 01' the character described comprising, a plurality of objects arranged to move in synchronism, synchronizing means interconnecting said objects, said synchronizing means including an alternating current s pp y, means fed therefrom for setting up an alternating reversible phase potential responsive to the departure of the objects from synchronism, means for modulating said alternating potential to convert the same into a reversible direct current potential, a second source oi alternating current supply, modulating mean fed from said second source of supply connected for receiving said reversible direct current signal and for converting the same back into a reversible phase alternating current signal, thermionic means for receiving said alternating current signal, a servomotor mechanism controlled from said alternating current signal including a motor for driving said controlled object, and a followup connection from said servomotor mechanism to said alternating, reversible phase potential setting up means.

2. In a positional follow-up control wherein a reversible motor drives a system into angular correspondence with a synchro transmitter, a transmitter, a driven system controlled therefrom and including a reversible power motor, means for producing a. reversible phase alternating current signal from relative displacement between the transmitter and the driven system, means for producing an alternating current carrier signal, means for combining said two signals'and for converting the displacement signal into a reversible direct current signal, a. thermionic tube circuit, means for impressing the direct current signal upon said thermionic tube circuit the output 01' which controls the speed and direction of rotation of the said reversible power motor, and a follow-up connection between said power motor and said displacement signal producing means.

3. A position control system of the character described comprising, a plurality oi! objects arranged to move in synchronism, synchronizing means interconnecting said objects, said synchronizing means including high speed and low speed transmitters and connected receiver arrangements for setting up alternating potentials responsive to the departure of said objects from synchronism, means for supplying an alternating potential, means connecting said last named means in series with theoutputs of said high speed and low speed transmitter and connected receiver arrangements, thermionic means fed from said connecting means and responsive to the combined potential carried thereby, motor means controlled from said thermionic means for causing said objects to return to synchronism, said added alternating potential serving to eliminate 180 embiguity of said controlled object with respect to said controlling object, and a follow-up connection between said motor means and said high and low speed receiver arrangements.

4. A position control system of the character described comprising, a plurality oi! objects arranged to move in synchronism, synchronizing means interconnecting said objects including a reversible motor for maintaining said objects in synchronism, said synchronizingmeans also including high speed and low speed transmitters and connected receiver arrangements for setting up alternating potentials responsive to the departure of said objects from synchronism, means for limiting the maximum potential output of said high speed transmitter-receiver arrangei ment, means for supplyin an alternating potential signal of substantially constant value, means for combining said three signals, and mean for impressing the resultant upon a thermionic tube circuit the output oi which controls the speed and direction of rotation of said reversible motor.

5. In a position control control system, in combination, controlling and controlled objects, a motor for driving said controlled object, thermionic tube means for controlling said motor, high speed and low speed transmitter operated from said controlling object, high speed and low speed receivers electrically connected to said transmitters, said receivers being arranged to be electrically connected to said thermionic tube means to supply signal voltages thereto, a voltage limiter arranged for connection to said thermionic tube means and connected in the output 0! at least' one of said receivers for limiting the signal voltage or the latter, means for adding an alternating current voltage in series with the outputs of said receivers to be supplied to said thermionic tube means, said added alternating current voltage serving to eliminate 180 ambiguity 01' said controlling and controlled objects, and a mechanical follow-up connection between said controlled object and said high and low speed receivers.

6. In a position control system, in combination, controlling and controlled objects, a motor for driving said controlled object, thermionic control means for said motor, high speed and low speed transmitters operated from said controlling object, high speed and low speed receivers electrically connected to said transmitters, means for limiting the output voltage of said high speed receiver, said receivers being arranged to be electrically connected to said thermionic control means to supply signal voltages thereto, means for adding an alternating current voltage in series with the outputs of said receivers to be supplied to said thermionic control means, and said added alternating current voltage serving to eliminate 180 ambiguity of said controlling and controlled objects, and a mechanical follow-up connection between said controlled object and said high and low speed receivers.

1. In a position control system, a transmitterreceiver arrangement for producing a reversible phase alternating current signal, a modulator and connected rectifier supplied from said arrangement and acting to convert the signal into a reversible direct current signal, a second modulator for re-converting said direct current signal back into a reversible phase alternating current signal, a servo system controlled from said last named signal, and a follow-up connection between said servo system and said transmitterreceiver arrangement.

8. In a positional iollow up control wherein a reversible motor drives a system into angular correspondence with a synchro transmitter, a transmitter, a driven system, a reversible motor for driving said system, means for producing a reversible alternating current signal from relative displacement between the transmitter and the driven system, means for producing a fixed alternating current signal, means for combining said two signals, a modulator supplied with a version of said combined signals and acting to convert the same into a direct current signal, a second modulator for reconverting .said direct current signal to a resultant alternating current 8 a thermionic tube circuit, means for impreuing the resultant alternating current signal upon said thermionic tube circuit the output of which controls the speed and direction of rotation of the said reversible motor, and a follow-up connection between said motor and said signal producing means.

9. In a positional control system, controlling and controlled objects, transmitter-receiver means for producing a signal potential dependent upon relative movement of said objects, thermionic tube means for receiving said signal potential and including grid controlled rectiflers connected in phase opposition, a reversible motor controlled from said thermionic tube means and mechanically connected for drivin the controlled object, transformers having their secondaries connected respectively in the plate circuits of said grid controlled rectiilers, said motor having phase windings connected respectively to the primary windings of said transformers, single phase supply leads connected respectively to the common point of said motor phase windings and to the common point of said transformer primaries, condenser means arranged to be selectively electrically connected to said phase windings dependent on which of said grid controlled rectlflers passes current, and a follow-up connection between said motor and said signal producing means. 7

,'10. A positional control system as defined in claim 9 wherein said condenser means is connected across the plates of said grid controlled rectiflers, and additional condenser means connected across the grids of said grid controlled rectiflers for correcting the phase relation of the plate-grid p tentials of the non-operating rectifler.

l2 ILApoltionalcontrolsystemasdeiinedin claim8,whereinsaidtbermionic tube circuithas meansforderivingaratesignalfromthedisplacement signal and means combining said rate signal with the displacement signal to produce a dead-beat control or said power motor.

12. In a positional control system, controlling and controlled oblects, transmitter receiver means for producing a signal potential dependent 10 upon relative movement of said obiects,push-pu1l thermionic tube means for receiving said signal potential. a pair of output transformer having primary windings connected to the outputs of said thermionic tube means, a reversible motor is having stator windings connected in series with the secondary windings of said transformer means, said motor being connected for driving the controlled obiect, a single phase supply for said motor, said motor having a condenser conn nected across its series connected stator windings, said thermionic tube means serving to short one or the other of said transformer secondary winding in eifect, to thereby selectively connect one of said stator windings directly across gs said single phase supply and the other of said winding across said supply in series with said condenlr, thereby eifecting reversible operation of said motor, and a follow-up connection between said motor and said transmitter-receiver means,

ERIC J. ISBIBTER. FRANCIS L. MOSELEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Hull Jan 19. 1937 

